By means of a continuous process, which is called pultrision, sections can be manufactured of reinforcement fibers which are impregnated with plastics (see e.g. V. Kerbiriou "Impragnieren und Pultrusion von thermoplastischen Verbundprofilen", VDI-Verlag, Dusseldorf 1997). The plastic is distributed between the fibers in the method in such a manner that a tight, pore-poor polymer matrix arises. The matrix consists of the plastic (matrix polymer) in the form of a largely homogeneous phase that is embedded between the fibers. As a starting product (semi-finished product) one advantageously uses bandlets, mixed fibers, powder impregnated fiber bundles or fiber bundles which are impregnated with flowable plastic which are manufactured from a compound material and which are already consolidated. Thermoplastics or duromers (to the extent that these are not yet hardened and are thus flowable) come under consideration for matrix polymers. In the pultrusion of compound materials with solid thermoplastics, for example the named bandlets, the plastics must first be melted. The fusion viscosity amounts to about 500 to 1000 Pa s. Known draw off speeds through a nozzle of the compound materials can be to up to 6 m/min. Greater speeds lead to losses in the pultrate quality as a result of faulty compression, insufficient distribution of the matrix polymer and/or fiber breakage.
A plant for carrying out a pultrusion comprises a supply device for the starting product, an oven, a nozzle (draw or shaping nozzle) and a draw off device, with the nozzle having a continuously narrowing cross-section in a shape-imparting region. The nozzle is slightly overfilled with the starting product so that a matrix flow-back within the fiber bed that is formed by the fibers takes place. The permeability of the fiber bed is anisotropic. The matrix flow takes place mainly along the fibers, but also transverse to the latter, through which the largely homogeneous distribution of the matrix polymer over the entire cross-section of the section that is to be achieved first results. Due to the matrix flow-back the fiber volume proportion increases in the nozzle and a surplus of plastic forms at the nozzle entry, which drips off there.